This patent deals generally with intrusion detection and more specifically with a circuit which responds to the radiant energy emitted by an intruder to activate an appropriate response.
Intruder detection circuits have become common household items, so much so that they are even used in situations which would not be considered "intrusions". The systems have become so commonplace and have been made so compact that they can now be used to replace common, everyday wall switches for the control of household lights.
In such situations, room or yard lights can be turned on, not only when some unwanted intruder activates the system, but also when residents merely walk through an area, thus automatically furnishing light only when it is needed, and turning the lights off automatically after a specific time period when no person's presence is detected.
However, this very increase in use brings greater demands for reliability and improved suppression of radio frequency interference. When each household has several such intrusion detectors everyone expects those lights to go on only when they are supposed to, and every time they are required to, and no one will tolerate the television picture being interfered with every time the kitchen lights go on.
Yet many existing detector circuits have just such problems. Sensitivity adjustments ca be difficult to set and may vary with room temperature, and radio frequency interference can make the use of radios and televisions difficult in proximity to a detector.